Remembering when I've put a custom email (amazon@mydomain) vs a plus (me+amazon@mydomain) not to mention remebering both that I've used something fancy and, how exactly I customized it has just caused a bunch of headaches. I have warranty purchases across multiple email addresses for sites, figuring out what to type into the "forgot my password" box is a pain...
I even have a Steam login that I can't for the life of me recall how to get into. I only know the username, but I don't know how to request the reset email associated with it. None of my guesses have worked. So ... I just made another Steam account.
... and ironically the email address I give to close friends is the one that's all over haveibeenpwned.com.
/facepalm